U.S. patent number 10,525,185 [Application Number 15/509,009] was granted by the patent office on 2020-01-07 for method of determining a system compressibility value of a medical membrane pump drive.
This patent grant is currently assigned to FRESENIUS MEDICAL CARE DEUTSCHLAND GMBH. The grantee listed for this patent is FRESENIUS MEDICAL CARE DEUTSCHLAND GMBH. Invention is credited to Frank Hedmann, Torsten Hochrein.
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United States Patent |
10,525,185 |
Hedmann , et al. |
January 7, 2020 |
Method of determining a system compressibility value of a medical
membrane pump drive
Abstract
A method of determining a system compressibility value of a
medical membrane pump drive is provided which includes moving to a
first and second pressure level and detecting a first and second
operating parameter value of the membrane pump drive. The system
compressibility value is determined on the basis of the detected
operating parameter values and the membrane of the membrane pump
drive is supported at a rigid surface during the determination of
the system compressibility value.
Inventors: |
Hedmann; Frank (Volkach,
DE), Hochrein; Torsten (Eschenau, DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
FRESENIUS MEDICAL CARE DEUTSCHLAND GMBH |
Bad Homburg |
N/A |
DE |
|
|
Assignee: |
FRESENIUS MEDICAL CARE DEUTSCHLAND
GMBH (Bad Homburg, DE)
|
Family
ID: |
54145723 |
Appl.
No.: |
15/509,009 |
Filed: |
September 3, 2015 |
PCT
Filed: |
September 03, 2015 |
PCT No.: |
PCT/EP2015/001782 |
371(c)(1),(2),(4) Date: |
March 06, 2017 |
PCT
Pub. No.: |
WO2016/034286 |
PCT
Pub. Date: |
March 10, 2016 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170290971 A1 |
Oct 12, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Sep 4, 2014 [DE] |
|
|
10 2014 013 152 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61M
1/3626 (20130101); F04B 43/067 (20130101); A61M
1/14 (20130101); A61M 1/281 (20140204); A61M
1/106 (20130101); F04B 51/00 (20130101); A61M
1/28 (20130101); A61M 1/1086 (20130101); A61M
5/36 (20130101); A61M 5/14593 (20130101); A61M
1/1006 (20140204); A61M 1/1037 (20130101); A61M
2205/3331 (20130101); A61M 5/1413 (20130101); A61M
2205/12 (20130101); A61M 2005/14513 (20130101) |
Current International
Class: |
A61M
1/00 (20060101); A61M 1/36 (20060101); F04B
43/067 (20060101); A61M 1/28 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
102725007 |
|
Oct 2012 |
|
CN |
|
103443610 |
|
Dec 2013 |
|
CN |
|
19919572 |
|
Nov 2000 |
|
DE |
|
102011105824 |
|
May 2012 |
|
DE |
|
WO 2013/176770 |
|
Nov 2013 |
|
WO |
|
Primary Examiner: Eisenberg; Rebecca E
Attorney, Agent or Firm: Jacobson Holman, PLLc.
Claims
The invention claimed is:
1. A method of determining a system compressibility value of a
medical membrane pump drive of a medical device, the membrane pump
drive including a membrane, a coupling surface for coupling a pump
cassette to the medical device, a drive chamber arranged in the
coupling surface, said drive chamber being closed by said membrane,
a piston-in-cylinder unit including a piston movable in a cylinder,
the cylinder connected to the drive chamber for adjusting a
pressure in the drive chamber by moving the piston, and a pressure
sensor for determining the pressure in the drive chamber, said
membrane being deflected outwardly out of the drive chamber by
excess pressure in the drive chamber and being deflected inwardly
into the drive chamber by negative pressure in the drive chamber,
the membrane being deformable from a flat configuration inwardly to
a first maximum deflection where the membrane contacts a first
rigid surface of the medical device and outwardly to a second
maximum deflection where the membrane contacts a second rigid
surface of the medical device or the pump cassette coupled to the
medical device, the method comprising: moving the piston of the
piston-in-cylinder unit to produce a first pressure level in the
drive chamber, said first pressure level exceeding a maximum
counter-pressure of the membrane such that the membrane is
deflected inwardly to the first maximum deflection in contact with
the first rigid surface or is deflected outwardly to the second
maximum deflection in contact with the second rigid surface;
detecting a first position of the piston of the piston-in-cylinder
unit of the membrane pump drive associated with the first pressure
level; moving the piston of the piston-in-cylinder unit to produce
a second pressure level in the drive chamber, the second pressure
level exceeding the maximum counter-pressure of the membrane such
that the membrane is still deflected inwardly to the first maximum
deflection in contact with the first rigid surface or is still
deflected outwardly to the second maximum deflection in contact
with the second rigid surface; detecting a second position of the
piston of the piston-in-cylinder unit of the membrane pump drive
associated with the second pressure level; and determining the
system compressibility value on the basis of the first and second
positions of said piston.
2. The method in accordance with claim 1, wherein the medical
device includes a pump cassette receiver having a receiving surface
supporting a rear side of the pump cassette when a front side of
the pump cassette is coupled to the coupling surface, the method
further comprising a step of coupling the pump cassette to the
membrane pump drive, with the cassette being received in the pump
cassette receiver in a coupled state; wherein the step of coupling
the pump cassette to the membrane pump drive is performed after the
step of determining the system compressibility value, and wherein
the second rigid surface in contact with the membrane during the
determination of the system compressibility value is the receiving
surface of the pump cassette receiver.
3. The method in accordance with claim 1, wherein the pump cassette
includes a pump chamber, the method further comprising a step of
coupling the pump cassette to the membrane pump drive; wherein the
step of determining the system compressibility value is performed
after the step of coupling the pump cassette to the membrane pump
drive and wherein the membrane is completely pressed into the pump
chamber of the pump cassette and being supported at a rear wall of
the pump chamber during the determining of the system
compressibility value, such that the second rigid surface is formed
by the rear wall of the pump chamber.
4. The method is accordance with claim 1, wherein the system
compressibility value is determined at a negative pressure, with
the membrane being completely drawn into the drive chamber of the
membrane pump drive and contacting a rear wall of the drive chamber
during the determining of the system compressibility value, such
that the first rigid surface is formed by the rear wall of the
drive chamber.
5. The method in accordance with claim 1, wherein the medical
device includes an air cushion via which, in normal operation, the
pump cassette is pressed toward the coupling surface of the
membrane pump drive from its rear side, wherein the method further
comprises the step of filling the air cushion to an operating
pressure before determining the system compressibility value.
6. The method in accordance with claim 1, wherein a difference
between the first and second pressure levels is greater than 5 mbar
and less than 500 mbar.
7. The method in accordance with claim 1, wherein a first system
compressibility value is determined at negative pressure values and
a second system compressibility value is determined at excess
pressure values.
8. The method in accordance with claim 1, wherein the system
compressibility value is determined in dependence on a difference
between the first position and the second position of the piston of
the piston-in-cylinder unit.
9. The method in accordance with claim 1, wherein the first
position and the second position of the piston of the
piston-in-cylinder unit is determined using a length sensor.
10. The method of claim 9, wherein the piston-in-cylinder unit and
the drive chamber are filled with hydraulic fluid.
11. The method in accordance with claim 1, comprising the further
steps of: coupling the membrane pump cassette to the membrane pump
drive; pumping a fluid through a pump chamber of the membrane pump
cassette by operating the membrane pump drive; moving the piston to
produce a third pressure level and a fourth pressure level in the
drive chamber; detecting a third position and a fourth position of
the piston associated with the third and the fourth pressure
levels, respectively; and determining at least one of an air
proportion and an air quantity in the fluid pumped through the pump
chamber of the membrane pump cassette on the basis of the third and
fourth positions of the piston.
12. The method in accordance with claim 11, wherein the system
compressibility value of the membrane pump drive is taken into
account in the determination of the at least one of the air
proportion and the air quantity; and wherein the third pressure
level is equal to the first pressure level and the fourth pressure
level is equal to the second pressure level.
13. The method of claim 1, wherein a transmission of pressure onto
the membrane takes place hydraulically.
14. A membrane pump drive of a medical device comprising: a
coupling surface for coupling a pump cassette to the membrane pump
drive; a drive chamber arranged in the coupling surface, said drive
chamber being closed by the membrane of said membrane pump drive,
said membrane being deflected outwardly out of the drive chamber by
excess pressure in the drive chamber and being deflected inwardly
into the drive chamber by negative pressure in the drive chamber,
the membrane being deformable from a flat configuration inwardly to
a first maximum deflection where the membrane contacts a first
rigid surface of the medical device and outwardly to a second
maximum deflection where the membrane contacts a second rigid
surface of the medical device or the pump cassette coupled to the
medical device; a piston-in-cylinder unit including a piston
movable in a cylinder, the cylinder connected to the drive chamber
for adjusting a pressure in the drive chamber by moving the piston;
a pressure sensor for determining the pressure in the drive
chamber; and a controller, said controller being configured to
carry out a method of determining a system compressibility value,
the method including the steps of moving the piston of the
piston-in-cylinder to produce a first pressure level in the drive
chamber, wherein the first pressure level exceeds a maximum
counter-pressure of the membrane such that the membrane is
deflected inwardly to the first maximum deflection in contact with
the first rigid surface or is deflected outwardly to the second
maximum deflection in contact with the second rigid surface;
detecting a first position of the piston of the piston-in-cylinder
unit of the membrane pump drive associated with the first pressure
level; moving the piston of the piston-in-cylinder unit to produce
a second pressure level in the drive chamber, the second pressure
level exceeding the maximum counter-pressure of the membrane such
that the membrane is still deflected inwardly to the first maximum
deflection in contact with the first rigid surface or is still
deflected outwardly to the second maximum deflection in contact
with the second rigid surface; detecting a second position of the
piston of the piston-in-cylinder unit of the membrane pump drive
associated with the second pressure level; and determining the
system compressibility value on the basis of the first and second
positions of the piston.
15. A blood treatment machine having a membrane pump drive in
accordance with claim 14.
16. The blood treatment machine of claim 15, wherein the blood
treatment machine is a dialysis machine.
17. The blood treatment machine of claim 15, further comprising a
pump cassette receiver and an air cushion for pressing the pump
cassette to the coupling surface of the membrane pump drive.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of determining a system
compressibility value of a medical membrane pump drive as well as
to a method of determining an air proportion and/or an air quantity
in a medical fluid conveyed by a membrane pump.
Membrane pumps are frequently used in the field of medical
engineering, and in particular in the field of dialysis technology,
to pump medical fluids such as dialyzate or blood. In this respect,
a membrane pump typically has a pump chamber closed by a membrane,
wherein fluid can be pressed out of the pump chamber by pressing
the membrane into the pump chamber and fluid can be sucked into the
pump chamber by pulling the membrane out of the pump chamber. Fluid
can hereby be pumped through the pump chamber in interaction with
corresponding valves.
The pump chamber is in this respect mostly arranged in a
disposable, for example in a pump cassette, that is coupled to a
membrane pump drive. The membrane pump drive in this respect
typically has a drive chamber that is likewise closed by a
membrane. The pump chamber and the drive chamber are then coupled
to one another such that the membrane of the pump chamber follows
the movement of the membrane of the drive chamber.
With a piston membrane pump, the drive chamber is in this respect
in hydraulic communication with a piston-in-cylinder unit.
Hydraulic fluid can be pressed into or sucked out of the drive
chamber by moving the piston, which has the consequence of a
corresponding movement of the membrane of the drive chamber. Such
an arrangement has the advantage that the pump pressure can be
controlled by a corresponding control or regulation of the pressure
in the hydraulic part. Furthermore, membrane pumps allow a simple
balancing of the pumped fluids since the volume change of the pump
chamber and thus the fluid displacement on a pump stroke
corresponds to the volume change of the control chamber (with the
opposite sign), wherein this can be determined exactly via the
position of the piston of the piston-in-cylinder unit.
Error sources can, however, occur here. On the one hand, air
collected in the pump chamber can have the result that the fluid
quantity pumped through the pump chamber does not exactly
correspond to the volume change of the drive chamber. Furthermore,
due to a certain system compressibility of the membrane pump drive,
the volume change of the control chamber can differ from the volume
change caused by the movement of the piston of the
piston-in-cylinder unit. In this respect, air that collects in the
hydraulic fluid can in particular result in a certain
compressibility of the hydraulic system. Furthermore, hoses that
connect the piston-in-cylinder unit to the drive chamber can, for
example, have a certain flexibility and therefore expand at an
elevated pressure. A certain system compressibility that influences
the values detected for the balancing can also occur with other
drive mechanisms.
2. Description of the Related Art
A method is in this respect known from DE 19919572 A1 by which the
air proportion can be determined in the fluid pumped through a pump
chamber. For this purpose, the pump chamber is first filled by
gravity and the starting pressure hereby resulting is measured. The
cut-off valves of the pump chamber are thereupon closed so that a
fluid volume enclosed therein results. With closed cut-off valves,
the piston-in-cylinder unit is then actuated to act on the closed
fluid volume with a predefined end pressure. The volume change of
the fluid volume in the pump chamber accompanying this pressure
change in this respect directly depends on the proportion of air in
the enclosed fluid volume. The air proportion can therefore be
determined with the aid of the volume change that is produced by
the pressure difference and that is determined via the piston
movement. In this respect, in DE 19919572 A1, the influence of the
system compressibility of the membrane pump drive is taken into
account by a fixedly predefined constant. However, the system
compressibility can, for example, vary due to air collecting in the
hydraulic fluid during the operation of the pump, which remains out
of consideration in DE 19919572 A1.
A method is therefore known from DE 102011105824 B3 how the system
compressibility of a membrane pump drive can be determined. In this
respect, the system compressibility of the pump apparatus filled
with gas is determined in that a start pressure and an end pressure
are adjusted using a pressure sensor and the associated pump
positions or pump sensor values are recorded. The spring constant
which is set as equivalent to the system compressibility is
determined on the basis of the value pairs.
SUMMARY OF THE INVENTION
In accordance with a first aspect, it is the object of the present
invention to provide an improved method of determining a system
compressibility of a medical membrane pump drive. In accordance
with a second aspect, it is the object of the present invention to
provide an improved method of determining an air proportion and/or
an air quantity in a medical fluid conveyed by a membrane pump. It
is furthermore the object of the present invention to provide
corresponding membrane pump drives or blood treatment machines
having corresponding membrane pump drives that carry out the
methods in accordance with the invention.
In accordance with the first aspect, the present invention
comprises a method of determining a system compressibility value of
a medical membrane pump drive in which a first and a second
pressure level are moved to and a first and second operating
parameter value of the membrane pump drive is detected, with the
system compressibility value being determined on the basis of the
detected operating parameter values. In accordance with the present
invention, the membrane of the membrane pump drive is in this
respect supported at a rigid surface during the determination of
the system compressibility value. The membrane of the membrane pump
drive can in particular be supported at a rigid surface in this
respect while the first and second operating parameter values
corresponding to the first and second pressure levels are
detected.
The present invention in this respect takes into account that a
membrane pump drive actually does not represent a closed system
whose total volume is unchangeable, but is rather coupled to
further system parts by the membrane of the membrane pump drive.
Since the membrane of the membrane pump drive is supported at a
rigid surface in accordance with the invention during the
determination of the system compressibility, the system
compressibility of the membrane pump drive can, however, be largely
sealed off from external influences. The system compressibility
value determined in accordance with the invention therefore more
exactly reproduces the compressibility going back to the membrane
pump drive itself. Furthermore, the determination in accordance
with the invention is no longer influenced by the counter-pressure
of the membrane of the membrane pump drive.
The system compressibility value in accordance with the invention
can in this respect be any desired parameter by which a
compressibility property or the yielding of the membrane pump drive
on pressure changes can be characterized and preferably quantified.
In this respect, the membrane pump drive positions associated with
the first and second pressure levels are used as the operating
parameter values from which the system compressibility value is
calculated.
To move to the first and second pressure levels, the membrane pump
drive is preferably actuated until the pressure of the membrane
pump and/or of the membrane pump drive reaches the first pressure
level. The first operating parameter value of the membrane pump
drive is thereupon determined. The membrane pump drive is then
actuated until the pressure of the membrane pump and/or of the
membrane pump drive reaches the second pressure level and then the
second operating parameter value is determined. The pressure of the
membrane pump drive and/or of the membrane pump can in this respect
be detected via a pressure sensor. The operating parameter can be
determined via a corresponding operating parameter sensor, for
example via a position sensor and/or a motion sensor.
The first and second pressure levels can in this respect be
predefined pressure levels. They can in particular be stored in a
control of the membrane pump drive.
In accordance with a preferred embodiment of the present invention,
the first and second pressure levels at which the operating
parameter values are determined exceed the maximum counter-pressure
of the membrane of the membrane pump drive. This provides that,
depending on whether work is being done at a vacuum or at excess
pressure, the membrane is either deflected outwardly or inwardly by
a maximum while the respective operating parameter value present at
the first and second pressure levels is determined.
The method in accordance with the invention is preferably used with
those system in which a pump cassette having a pump chamber
arranged therein is couplable to the membrane pump drive.
In accordance with a first variant of the present invention, the
determination of the system compressibility value can take place in
this respect before the pump. cassette is coupled. The membrane in
this case preferably contacts a receiving surface of a pump
cassette receiver during the determination of the system
compressibility value. Such a pump cassette receiver is in this
respect used in normal pump operation to hold the pump cassette at
the coupling surface of the membrane pump drive. For this purpose,
it has a receiving surface at which the rear wall of the pump
chamber is supported in the inserted state of the pump cassette. In
accordance with the present invention, the determination of the
system compressibility value can now take place before the pump
cassette has been inserted, with the membrane in this respect
contacting this receiving surface. The receiving surface can in
this respect, for example, approximately follow the shape of the
pump chamber and typically has a concave shape.
In a second variant of the present invention, the determination of
the system compressibility value can take place with a coupled pump
cassette. In this respect, the membrane of the membrane pump drive
can be completely pressed into the pump chamber of the pump
cassette during the determination of the system compressibility
value and can be supported at the rear wall of the pump chamber.
The membrane of the membrane pump drive in this state contacts the
membrane of the pump cassette that in turn contacts the rear wall
of the pump chamber.
The determination of the system compressibility value preferably
takes place at excess pressure in the two above-described variants.
The membrane of the membrane pump drive is hereby pressed out of a
drive chamber toward the corresponding counter-surface.
The determination of the system compressibility value can, however,
also take place by applying a vacuum. The membrane is in this
respect preferably drawn completely into the drive chamber of the
membrane pump drive and contacts a rear wall of this drive chamber.
The influence of further components on the determination of the
system compressibility value of the membrane pump drive can hereby
also be reduced or avoided.
The present invention can in particular be used in such membrane
pump drives in which, in normal operation, the pump cassette is
pressed toward a coupling surface of the membrane pump drive by the
pressurizing of an air cushion arranged behind the pump cassette. A
pump cassette receiver into which the pump cassette is inserted in
normal operation can in this respect in particular be moved
together with the pump cassette toward the coupling surface of the
membrane pump drive due to the filling of the air cushion.
The determination of the system compressibility value in this
respect preferably takes place after the air cushion has been
filled to operating pressure. This is of advantage independently of
whether the system compressibility value is determined with or
without an inserted pump cassette since it is ensured by the
filling of the air cushion that the counter-surface the membrane
contacts does not move. A mechanical clearance that is present
without the pressing on and a mechanical deformation is in
particular hereby reduced or avoided during the measurement. The
operating pressure of the air cushion is in this respect preferably
greater than the first and second pressure levels and/or the force
exerted onto the pump cassette receiver by the air cushion is
greater than the force exerted by the first and second pressure
levels via the membrane of the membrane pump drive such that the
exact level of the operating pressure has no influence on the
determination of the system compressibility.
The determination of the system compressibility at vacuum can in
this respect take place both with an inserted pump cassette and
before the insertion of the pump cassette.
If the determination of the system compressibility value takes
place with an inserted cassette, at least one valve of the pump
chamber is preferably open to allow a fluid flow into or out of the
pump chamber when the membrane contacts the rear wall of the drive
chamber or of the pump chamber on the moving to the first operating
pressure.
The first pressure level used in accordance with the invention is
preferably greater than 50 mbar since the typically used membranes
typically generate a counter-pressure of approximately 50 mbar. The
first pressure level is preferably greater than 75 mar, further
preferably greater than 100 mbar, and further preferably greater
than 150 mbar. It is hereby ensured that the membrane is completely
laid against the counter-surface on the reaching of the first
pressure level. The first pressure level is, however, preferably
less than 600 mbar. It is hereby ensured that the system
compressibility value is measured in a pressure range that also
occurs in the normal pump operation of the pump. The first pressure
level is in this respect preferably smaller than 400 mbar, further
preferably smaller than 300 mbar, and further preferably smaller
than 250 mbar. A certain pressure value range above the first
pressure level is hereby still provided to move to the second
pressure level.
The second pressure level is preferably likewise greater than 50
mbar, further preferably greater than 200 mbar, further preferably
greater than 250 mbar. It is hereby achieved that the membrane is
fully placed on. The second pressure level is in this respect
preferably higher than the first pressure level. The second
pressure level is, however, preferably smaller than 600 mbar,
preferably smaller than 500 mbar, further preferably smaller than
450 mbar, further preferably smaller than 400 mbar. The measurement
range for the determination of the system compressibility value is
hereby held in a pressure range that is also reached in normal pump
operation.
The above-indicated pressure values are in this respect indicated
as absolute values of the pressure difference via the membrane,
i.e. the pressure difference between the pressure in the drive
chamber and the pressure that is applied at the outer surface of
the membrane. It can therefore be an excess pressure or a vacuum at
the indicated level. In this respect, atmospheric pressure is
preferably applied at the outer surface of the membrane while the
system compressibility value is determined.
The difference between the first and second pressure levels is
further preferably greater than 5 mbar, further preferably greater
than 10 mbar, further preferably greater than 40 mbar, further
preferably greater than 80 mbar. A certain precision in the
determination of the system compressibility value is ensured by a
sufficiently large pressure difference between the first and second
pressure levels. If, in contrast, the pressure difference is
selected as too small, it only corresponds to a minimal change of
the pump drive position, which increases the influence of
measurement errors.
The difference between the first and second pressure levels,
however, is preferably smaller than 500 mbar, preferably smaller
than 400 mbar, further preferably smaller than 300 mbar, further
preferably smaller than 200 mbar. Pressure levels can hereby be
selected that are in the normal operating range of the pump drive
during pumping. The measurement can furthermore take place
fast.
For example, the first pressure level can amount to approximately
200 mbar and the second pressure level to approximately 300
mbar.
Provision can be made in accordance with the method in accordance
with the invention that a system compressibility value is
determined both at vacuum and at excess pressure. Effects can
hereby be taken into account that have different effects on the
system compressibility value at vacuum and at excess pressure.
As already presented above, any desired parameter can be determined
as the system compressibility value that is correlated with the
yielding of the pump drive on a pressure change. The system
compressibility value in this respect particularly preferably
depends on the difference of the operating parameter values that
are determined at the first and second pressure levels. The system
compressibility value is in this respect in particular determined
using this difference.
The system compressibility value in this respect preferably depends
on the difference between the pump positions that the membrane pump
drive adopts at the first and second pressure levels. The system
compressibility value can in particular be simply determined as
this difference.
The method in accordance with the invention is preferably used with
a membrane pump drive that has a drive chamber that is closed by
the membrane, with the membrane being deflected outwardly out of
the drive chamber by excess pressure in the drive chamber and being
deflected inwardly into the drive chamber by a vacuum in the drive
chamber.
The membrane pump drive can furthermore have a pressure sensor that
determines the pressure in the drive chamber to move to the first
and second pressure levels.
The pressure in the drive chamber can furthermore preferably be
produced via a piston-in-cylinder unit in communication with the
drive chamber. The piston-in-cylinder unit can in this respect in
particular be in fluid communication with the drive chamber, for
example via a connection hose. A length sensor is further
preferably provided that detects the position of the piston as an
operating parameter value.
The transmission of the pressure onto the membrane preferably takes
place hydraulically. The piston-in-cylinder unit and the working
chamber can in particular be hydraulically connected to one
another.
As already stated above, the main factors of influence for the
system compressibility with such an embodiment of the membrane pump
drive as a piston membrane pump are the air that has collected in
the hydraulic fluid of the hydraulic system and the yielding of the
connection hose between the piston-in-cylinder unit and the drive
chamber. This system compressibility can now be determined in
accordance with the invention without external values falsifying
the measured value via the membrane.
The present invention further comprises a membrane pump drive
having a pressure sensor and having a control, wherein the control
has a function for carrying out a method in accordance with the
invention such as was described above. The function can in this
respect in particular automatically determine the system
compressibility value of the membrane pump drive. The control can
move to the first and second pressure levels for this purpose and
can detect the associated first and second membrane pump drive
values, with the pressure levels being selected such that the
membrane is supported on a rigid surface.
The determination of the system compressibility value in this
respect in particular takes place in the activation phase, i.e.
before the actual pump operation. The function in accordance with
the invention can in this respect be integrated into the activation
routine. The function in accordance with the invention can in this
respect in particular carry out the determination of the system
compressibility value in an automated manner as part of the
activation routine and/or in response to a user input.
The membrane pump drive preferably furthermore has a sensor for
determining an operating parameter value, in particular a position
sensor for determining a membrane pump drive position.
The membrane pump drive furthermore preferably has a coupling
surface to which a pump cassette can be coupled.
The membrane pump drive is in this respect preferably designed such
as was already presented in more detail above with respect to the
method in accordance with the invention. It is in particular the
drive of a piston membrane pump. The function furthermore
preferably carries out the method in accordance with the invention
such as has already been presented above.
The present invention furthermore comprises a blood treatment
machine, in particular a dialysis machine, in particular a
peritoneal dialysis machine, having such a membrane pump drive. The
blood treatment machine in this respect in particular has a pump
cassette receiver and/or an air cushion for pressing the pump
cassette toward a coupling surface of the membrane pump drive. The
control of the membrane pump drive is in this respect preferably
integrated into the control of the blood treatment machine such
that it has a function for carrying out the method in accordance
with the invention.
In accordance with a second aspect, the present invention comprises
a method for determining an air proportion and/or an air quantity
in a medical fluid conveyed by a membrane pump. For this purpose, a
first and a second pressure level are moved to by a corresponding
control of a membrane pump drive of the membrane pump and
associated operating parameter values of the membrane pump are
detected, with the air proportion and/or the air quantity being
determined on the basis of the operating parameter values. Unlike
in accordance with the methods known from documents DE 19919572 A1
and DE 102011105824 B3, it is thus not the pressure level randomly
resulting from the gravity filling of the pump chamber that is used
as the starting pressure as the first pressure level, but rather a
predefined pressure level moved to by a corresponding control of
the membrane pump drive. The determination of the air proportion or
of the air quantity is hereby independent of the pressure being
randomly adopted in the pressure chamber during the gravity
filling.
The determination of the air proportion and/or of the air quantity
preferably takes place in that all the valves of the pump chamber
are closed after the filling of the pump chamber such that a closed
fluid volume within the pump chamber results. The first pressure
level is thereupon first moved to and the first operating parameter
value is determined by a corresponding control of the membrane pump
drive and then the second pressure level is moved to and the
associated second operating parameter value is determined by a
repeat control of the membrane pump drive. The air proportion
and/or the air quantity can in this respect preferably be
determined with reference to the first and second pressure levels
as well as to the first and second operating parameter values.
A pump position is in this respect preferably determined as the
operating parameter value. The position of the piston of the
piston-in-cylinder unit can in particular be determined as the
operating parameter value for this purpose with a piston membrane
pump.
The calculation of the air proportion and/or of the air quantity
can then take place in accordance with the formula already known
from DE 19919572 A1.
The method in accordance with the invention is in this respect
preferably used such as has already been described above in detail
with respect to the first aspect. It can in particular be a piston
membrane pump. The method in accordance with the invention can in
this respect, however, be used independently of the determination
of a system compressibility value presented there.
However, a system compressibility value of the membrane pump drive
is preferably taken into account in the determination of the air
proportion and/or of the air quantity in accordance with the second
aspect. The accuracy in the determination of the air proportion
and/or of the air quantity is hereby increased.
In this respect, a third and fourth pressure level are preferably
moved to and associated operating parameter values of the pump are
detected for determining the system compressibility value, with the
system compressibility value being determined on the basis of the
operating parameter values. The operating parameter vales can in
turn be operating parameter values that are used for determining
the air proportion and/or air quantity. The determination of the
system compressibility value in this respect preferably takes place
in the activation phase of the membrane pump.
The same two pressure levels that are also used in the
determination of the air proportion and/or the air quantity are
preferably used in the determination of the system compressibility
value. This has the great advantage that the system compressibility
value does not have to be determined for a plurality of pressure
levels or pressure changes, but only for the first and second
pressure levels and that nevertheless correctly reproduces the
proportion of the system compressibility in the values measured in
the determination of the air proportion and/or air quantity. This
procedure is in this respect only made possible by the method in
accordance with the invention for determining the air proportion
and/or the air quantity in accordance with the second aspect of the
present invention according to which the first and second pressure
levels are actively moved to such that two predefined pressure
levels can be used here that are also used in the determination of
the system compressibility value.
In this respect, the method in accordance with the invention for
determining a system compressibility value in accordance with the
first aspect of the invention is preferably used for determining
the system compressibility value that is taken into account within
the framework of the determination of the air proportion and/or of
the air quantity in accordance with the second aspect.
The present invention furthermore comprises a membrane pump drive
having a pressure sensor and having a control, with the control
having a function for carrying out a method in accordance with the
invention for determining an air proportion and/or an air quantity
in accordance with the second aspect of the present invention. The
control in this respect preferably carries out the method in
accordance with the invention in an automated manner, in particular
during the ongoing pump operation. The air proportion hereby
determined and/or the air quantity hereby determined can in this
respect in particular be taken into account in the balancing of the
fluid conveyed by the membrane pump.
The membrane pump drive preferably has a coupling surface to which
a pump cassette can be coupled. The membrane pump drive further
preferably has a sensor for determining an operating parameter
value, in particular a sensor for determining a pump drive
position.
The membrane pump drive in accordance with the invention is
preferably designed in this respect such as has already been
presented above with respect to the method in accordance with the
invention in accordance with the first aspect of the present
invention.
The control of the membrane pump drive in accordance with the
invention particularly preferably has both a function for carrying
out a method for determining a system compressibility value in
accordance with the first aspect and a function for determining an
air proportion and/or an air quantity in the medical fluid conveyed
by the membrane pump drive in accordance with the second aspect of
the present invention.
The present invention furthermore comprises a blood treatment
machine, in particular a dialysis machine, in particular a
peritoneal dialysis machine, having a membrane pump drive in
accordance with the first and/or second aspects.
The blood treatment machine preferably has a pump cassette receiver
and/or an air cushion for pressing the pump cassette toward a
coupling surface of the membrane pump drive.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the present invention will now be
presented in more detail with reference to Figures and embodiment
examples.
There are shown:
FIG. 1: a schematic representation of a membrane pump drive in
accordance with the invention with a coupled pump chamber;
FIG. 2: a section through the coupling region of a membrane pump
drive in accordance with the invention with a coupled pump
cassette; and
FIG. 3: am embodiment of a pump cassette such as can be coupled to
a membrane pump drive in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Further scope of applicability of the present invention will become
apparent from the detailed description given hereinafter. However,
it should be understood that the detailed description and specific
examples, while indicating preferred embodiments of the invention,
are given by way of illustration only, since various changes and
modifications within the spirit and scope of the invention will
become apparent to those skilled in the art from this detailed
description.
FIG. 1 shows an embodiment of a membrane pump drive 30 in
accordance with the invention for a pumping of a medical fluid
through the pump chamber 4 that is couplable to the membrane pump
drive.
The membrane pump drive has a drive chamber 1 at which a flexible
membrane 2 is arranged. The flexible membrane 2 is arranged in a
coupling surface 3 of the membrane pump drive such that a membrane,
not recognizable in FIG. 1, of the pump chamber 4 can be coupled to
the membrane 2 of the drive chamber such that it follows the
movements of the membrane 2 of the drive chamber. The volume of the
pump chamber 4 can therefore be varied by a movement of the
membrane 2 out of or into the drive chamber 1. Fluid can be pumped
by the pump chamber 4 by moving the membrane 2 by the corresponding
switching of valves, not shown in any more detail in FIG. 1, that
control the inflow or outflow to or from the pump chamber 4.
The pump chamber 4 is in this respect typically part of a pump
cassette not shown in any more detail in FIG. 1 that preferably
represents a disposable. In this respect, the pump chamber is
typically formed by a corresponding shaping of a hard part of the
pump cassette that is covered by a flexible film forming the
membrane of the pump chamber.
The present invention would, however, also be usable in the same
way for membrane pumps in which the drive chamber and the pump
chamber are fixedly connected to one another or are integrated in a
common pumping apparatus.
In the embodiment shown in FIG. 1 it is in this respect a piston
membrane pump that has a piston-in-cylinder unit 7 that is in
hydraulic communication with the drive chamber 6 via the hydraulic
line 12. The piston-in-cylinder unit 7 is in this respect driven by
a drive 10 that acts on the piston 8 of the piston-in-cylinder unit
7 and moves it in the cylinder 9. The distance the piston 8 is
traveled in the cylinder 9 is detected or measured by a length
sensor 11 associated with the piston-in-cylinder unit 7.
The pressure side 25 of the piston-in-cylinder unit 7 is in this
respect in fluid communication with the drive chamber 1 via the
fluid line 12, with the pressure side 25, the fluid line 12 and the
drive chamber 1 being filled with hydraulic fluid. The adjustment
movement of the piston 8 is hereby transmitted to the membrane 2 of
the drive chamber 1. The membrane 2 of the drive chamber 1 is
therefore arched convexly outwardly or is pulled concavely into the
inner space of the drive chamber on a corresponding change of the
hydraulic volume of the piston-in-cylinder unit 7 by moving the
piston 8.
The volume change of the drive chamber 1 required for the fluid
conveying in the pump chamber 4 is accordingly brought about by
actuating the piston-in-cylinder unit 7. The hydraulic fluid is
pressed into or sucked out of the drive chamber 1 by actuating the
piston 8. The membrane 2 is hereby actuated whose movement is
transmitted onto the pump chamber 5 and varies its volume.
The membrane pump drive furthermore has a pressure sensor 13 via
which the pressure of the hydraulic fluid in the hydraulic system
and thus the pressure in the drive chamber 1 can be measured. The
pressure prevailing in the drive chamber 1 in this respect
corresponds--with the exception of a possible counter-pressure of
the membrane 2--to the counter-pressure prevailing in the pump
chamber 4 such that the pressure in the pump chamber 4 can also
simultaneously be determined via the pressure sensor 13.
The membrane pump drive furthermore has a control, not shown, that
is connected to the length sensor 11 and to the pressure sensor 13
and evaluates the measured signals. The control furthermore
controls the drive 10 of the membrane pump drive and the valves for
controlling the fluid flow into and out of the pump chamber 4.
Such a piston membrane pump has the advantage that it conveys fluid
with a very exact quantity, with the totally conveyed quantity
being able to be precisely balanced since the pump volume
corresponds to the stroke volume of the piston-in-cylinder unit 7
and can be exactly measured by the length sensor 11.
The control of the membrane pump drive of the present invention in
this respect first has a function in accordance with the second
aspect of the present invention by which an air proportion and/or
an air quantity in the fluid conveyed by the membrane pump can be
determined. It can be prevented by this function that air bubbles
that are present in the pump chamber 4 falsify the balancing of the
fluid conveyed through the air chamber 4.
A measurement phase that can be interposed between the pumping
process with every stroke is provided for determining the air
proportion or the air quantity. First, in this respect, fluid is
sucked into the pump chamber 4 by moving the membrane 2 in
accordance with the usual pumping process. The cut-off valves of
the pump chamber 4 are thereupon closed such that a closed fluid
volume results and a first, predefined pressure level p.sub.a is
moved to and the associated position of the piston 8 is determined
by actuating the drive 10. A second pressure level p.sub.e is
thereupon in turn traveled to and the associated position of the
piston 8 is likewise determined by actuating the drive 10. If the
fluid enclosed in the pump chamber 4 has a certain gas proportion,
it is compressed by the pressure increase, which corresponds to a
corresponding change of the volume of the pump chamber 4. This
volume difference can be determined by the positions of the piston
9 present at the starting pressure and at the end pressure.
The control calculates the air quantity contained in the pump
chamber from the values thus acquired, i.e. the air volume V.sub.at
contained there at atmospheric pressure. For this purpose, the
control assumes Boyle's law that reads for an isothermal state
change, i.e. while neglecting a temperature change:
p.times.V=constant.
Starting from this, different states of the measurement phase can
be equated to:
V.sub.at.times.p.sub.at=V.sub.a.times.p.sub.e=V.sub.e.times.P.sub.e.
While observing the relationship that the difference volume
V.sub.diff is determined by the difference of the starting volume
and of the end volume, that is V.sub.diff=V.sub.a-V.sub.e, the
actual gas volume at atmospheric pressure V.sub.at can be acquired
therefrom:
##EQU00001##
Depending on the specifically used pump method, it must be taken
into account with this formula that the pressure measured on the
hydraulic side of the membrane pump via the pressure sensor 13 may
not exactly correspond to the pressure in the pump chamber 4, but
differs by a specific value from this pressure due to the tension
of the membrane 2. In a first variant of the method, the
determination of the air proportion can, however, take place with a
non-deflected membrane 2 so that the influence of the membrane can
be neglected. In a second variant, the starting pressure p.sub.a
can in contrast be corrected by a difference pressure p.sub.mem due
to the membrane between the hydraulic side and the pump side. It
can be stored in the control, for example. It is hereby possible to
carry out the determination of the air proportion while the
membrane 2 has been drawn very far into or completely into the
drive chamber 1 such that the complete pump volume is utilized. The
differential pressure p.sub.mem between the hydraulic side and the
pump side due to the membrane can in this respect be determined in
the activation phase. Depending on the ratio between the pressures
on the hydraulic side and the differential pressure p.sub.mem due
to the membrane and the required precision, the differential
pressure p.sub.mem can optionally also be neglected, however.
The volume difference entering into the above formula is determined
by the distance of the piston S.sub.diff covered on the compression
from the pressure level p.sub.a to the pressure level p.sub.e, and
its area A.sub.K.
However, it must be taken into account in this respect that the
movement of the piston 8 on the pressure change from p.sub.a to
p.sub.e is not exclusively due to the air volume in the pump
chamber 4. For the membrane pump drive itself also has a certain
yielding or system compressibility under pressure changes. Factors
are in this respect in particular the air that can collect in the
hydraulic system and a certain flexibility of the hydraulic line
12. The piston 8 would therefore move by a certain distance S.sub.0
solely due to this system compressibility on a pressure change from
p.sub.a to p.sub.e even if no air at all were contained in the pump
chamber 4 and the latter were thus non-compressible.
The actual volume V.sub.at of the air contained in the pump chamber
4 thus results while taking account of the system compressibility
value S.sub.0 characterizing the system compressibility.
##EQU00002##
Since, in accordance with the second aspect of the present
invention, two previously fixed pressure levels p.sub.a and p.sub.e
are actively traveled to on the determination of the air volume in
the pump chamber 4, the system compressibility value S.sub.0
characterizing the system compressibility can be determined exactly
for this pressure change. Inaccuracies that resulted in accordance
with the prior art due to the use of the pressure level obtained by
gravity filling as the starting pressure level p.sub.a are hereby
avoided.
The control of the membrane pump drive in accordance with the
invention in this respect preferably has a second function via
which the system compressibility value S.sub.0 can be determined.
The first and second pressure levels p.sub.a and p.sub.e are also
moved to, for example in the activation phase, for this purpose and
the corresponding positions of the piston 8 are detected. In order
in this respect only to take effects into consideration that are
due to the system compressibility of the membrane pump drive and
not for instance to the compressibility of the components coupled
to the membrane pump drive, the determination takes place in a
state of the membrane pump drive in which the membrane 2 is
supported at a rigid surface. This can be achieved, for example, in
that the determination of the system compressibility value takes
place in a pressure range in which the membrane 2 has been
deflected to a maximum outwardly or inwardly.
The determination of the system compressibility value can in this
respect take place both with a pump cassette coupled to the
coupling surface 3 of the membrane pump drive and without a coupled
pump cassette.
The mechanical design of an embodiment of a membrane pump drive in
accordance with the invention to which a pump cassette can be
coupled is in this respect shown in more detail in FIG. 2. The
membrane pump drive has a machine block 20 at which the coupling
surface 3 is arranged for coupling the pump cassette 14. The drive
chamber 1 provided with the flexible membrane 2 is in this respect
let into the coupling surface 3 and is in hydraulic communication
with the piston-in-cylinder unit 7, not shown in any more detail
here, via the hydraulic line 12 with fluid 19.
The pump cassette 14 is in this respect inserted into a pump
cassette receiver 15 for coupling to the coupling surface 3 such
that the rear side of the pump cassette is supported at a receiving
surface of the pump cassette receiver 15. The receiving surface in
this respect has a corresponding spherically shaped cut-out for
this purpose in the region of the pump chamber 4 that is designed
as a bulge of the rear side of the pump cassette.
After the insertion of the cassette 14, the cassette receiver 15 is
pressed toward the coupling surface 3 via an air cushion 18 that is
arranged at the rear side and that is in turn supported at a device
wall 17. For this purpose, the air cushion is acted on by a
corresponding operating pressure that can be, for example, between
1,500 and 2,500 mbar.
In the embodiment, the pump cassette receiver 15 is designed as a
drawer that can be moved in and out in the direction 21 to insert a
cassette. The machine block 20 can furthermore be placed onto the
pump cassette 14 in the direction of movement 22. After the pushing
in of the drawer 15 and the placing on of the machine block 20, the
air cushion 18 is then pressurized to achieve a secure coupling of
the pump cassette 14 to the coupling surface 3.
Alternatively to the constructive design shown in FIG. 2, the pump
cassette receiver 15 could, however, also be designed as a door,
for example, that is opened for inserting the pump cassette 14 and
is closed for placing the pump cassette 14 at the coupling surface.
The air cushion 18 would be integrated into the door in this
case.
In this respect, an embodiment of a pump cassette 14 is shown in
FIG. 3 that has two pump chambers 4 and 4'. The pump cassette in
this respect comprises a hard part into which the fluid-conducting
channels and the pump chambers are let and is covered by a flexible
film with respect to the coupling surface. The pump cassette in
this respect inter alia has the valves 23 and 24 via which the
fluid flow into and out of the pump chambers 4 and 4' can be
controlled. The valves are in this respect likewise actuated via
actuators arranged in the machine block 20.
The determination in accordance with the invention of the system
compressibility value in this respect preferably takes place in the
activation phase of the membrane pump, but can in this respect be
carried out both with an inserted pump cassette and without an
inserted pump cassette.
If the determination is carried out as long as no pump cassette 14
was inserted, the membrane is supported on the receiving surface 16
of the pump cassette receiver 15 during the carrying out of the
measurements. If in contrast the determination is carried out with
an inserted pump cassette, the membrane 2 is supported on the rear
wall 5 of the pump chamber 4 and thus on the hard part of the pump
cassette. With an inserted pump cassette, at least one of the
valves that control the fluid flows into and out of the respective
pump chamber has to be open for this purpose. The determination of
the system compressibility value in this respect advantageously
takes place before the filling of the pump cassette with fluid or
while the pump chamber is in communication, for example, with the
dialysis bag or the drainage back via the fluid connections.
The fact that the membrane contacts the receiving surface 16 of the
pump cassette receiver or the rear wall of the pump chamber during
the measurement phase is achieved by correspondingly high pressure
levels p.sub.a and p.sub.e that provide a complete deflection of
the membrane during the measurement process. The tension of the
membrane 2 is in this respect already completely overcome by the
reaching of the first pressure level p.sub.a. On the pressure
increase to the second pressure level p.sub.e, the membrane is then
supported on a rigid counter-surface such that the membrane or
components coupled thereto has/have no influence on the
determination of the system compressibility value.
Since the tension of the membrane 2 is overcome at a pressure level
of approximately 50 mbar, a suitable first pressure level lies at
approximately 200 mbar; a suitable second pressure level at
approximately 300 mbar.
In this respect, the same pressure levels are preferably used for
determining the system compressibility value that are also used for
determining the air volume in the fluid conveyed by the pump. The
distance the piston 8 covers on the pressure increase from p.sub.a
to p.sub.e can hereby simply be used as the system compressibility
value S.sub.0. The system compressibility value S.sub.0 thus
results as the difference from the position values of the membrane
pump drive determined from the pressure levels p.sub.a and
p.sub.e.
As already presented above, the air content of the hydraulic fluid
and the stiffness of the hydraulic hoses represent the main
influence factors on the system compressibility. However,
mechanical tolerances and a deformation of the mechanical
components can also result in a certain yielding of the system and
thus in an increase in the system compressibility value.
The determination of the system compressibility value therefore
preferably takes place after the air cushion 18 has been filled to
the operating pressure such that the pump cassette receiver 15 is
pressed toward the coupling surface 3. The influence the clearance
of the pump cassette receiver and a possible mechanical deformation
of the involved mechanical components could have on the
determination of the system compressibility value is hereby
reduced. In addition, the determination of the system
compressibility value hereby takes place in the same situation that
is then also present in the determination of the air proportion
during the pump operation. The pump cassette receiver is in this
respect pressed toward the coupling surface via the air cushion 18
independently of whether the determination of the system
compressibility value is carried with or without an inserted pump
cassette.
To the extent that the system compressibility value is in this
respect influenced by the operating pressure of the air cushion,
the regulation tolerance of the internal air cushion pressure can
be restricted for a further increase in the accuracy.
In accordance with the above-described variants, the determination
of the system compressibility value takes place at excess pressure
such that the membrane 2 arches outwardly out of the drive chamber
1 and is supported on an outwardly arranged counter-surface.
The determination in accordance with the invention of the system
compressibility value can, however, also be reached at vacuum
levels. In this case, the vacuum levels are selected such that the
membrane 2 is supported on the rear wall 6 of the drive chamber 1.
A suitable first pressure level is in this respect approximately
-200 mbar; a suitable second pressure level approximately -300
mbar. The suitable vacuum levels thus correspond by amount to the
suitable excess pressure levels.
In the event that the determination of the system compressibility
value takes place at vacuum levels p.sub.a and p.sub.e, work is
preferably also carried out in accordance with the above-shown
second aspect with vacuum levels p.sub.a and p.sub.e to determine
the air volume in the fluid pumped through the pump chamber.
If work is carried out in this respect with vacuum levels on the
determination of the system compressibility value, the mechanical
properties of the design of the air cushion, the pump cassette
receiver and the machine block do not affect the measurement.
Provision can furthermore be made in accordance with the invention
respectively to determine a system compressibility value with
excess pressure levels and with vacuum levels. The mechanical
properties of the design of the air cushion, the pump cassette
mount and the machine block can be determined by the use of both
methods and they can be separated from the properties due to the
hydraulic system.
The determination of the system compressibility value at vacuum can
likewise take place with or without an inserted pump cassette. If
it takes place with an inserted pump cassette, the valves with
which the pump chamber communicates with further components should
be open.
The system compressibility value determined in accordance with the
invention can in this respect, on the one hand, enter into the
determination of the air volume of the conveyed medical fluid as
shown above. It in this respect allows a more exact balancing of
the fluids moved through the membrane pump since the air volume in
the pumped fluids can be determined more precisely.
The determination of the system compressibility value can
furthermore be used to verify the quality of the degassing of the
hydraulic system. In this respect, for example, as soon as the
system compressibility value exceeds a certain threshold, a
degassing of the hydraulic system can be carried out or its
necessity can be displayed.
The membrane pump drive in accordance with the invention is
preferably used in a blood treatment device for pumping medical
fluids, in particular for pumping blood or dialyzate. The membrane
drive pump in accordance with the invention is in this respect
particularly preferably used in a dialysis machine, with the
membrane pump being used for pumping the dialyzate into the abdomen
of the patient or for removing the dialyzate from the abdomen of
the patient.
The invention being thus described, it will be apparent that the
same may be varied in many ways. Such variations are not to be
regarded as a departure from the spirit and scope of the invention,
and all such modifications as would be recognized by one skilled in
the art are intended to be included within the scope of the
following claims.
* * * * *